In order to shore up a roof or a wall of a mine tunnel or gallery, or to prevent the premature disintegration of a mine face, it is customary to drill bores into such a rock formation and to insert bolts or studs into these bores where they are held in position by a suitable bonding agent such as, for example, a cementitious mass known as shotcrete. A bolt thus cemented in place can also be used as an anchor for a load-supporting member, e.g. a retainer for a carriage rail or for a supply conduit.
With two-component bonding agents, such as a liquid resin and a hardener therefor, it is convenient to seal the components in a frangible cartridge which is lodged in the bore and is ruptured by a rock bolt subsequently driven into that bore; see, for example, British Pat. No. 1,408,366 and U.S. Pat. No. 4,132,080. It is also known, e.g. from U.S. Pat. No. 3,892,101, to supplement the bonding agent by a charge of solid balls or the like designed to stabilize the bolt in the bore, especially when that bore is horizontal. It has further been proposed (Austrian Pat. No. 259,462) to use as an anchor member an internally threaded tube which is completely received in the bore and has apertured wall portions surrounded by elastic rings serving as one-way valves through which a hardenable bonding substance can escape into a surrounding clearance after being injected under pressure into the tube; the entrance end of the tube, located well inside the bore, is enveloped by an inflated seal to prevent the escape of any bonding agent from that clearance. Still another proposal (USSR Pat. No. 601,425) involves the axial shifting of a bolt provided with peripheral camming surfaces for forcing the surrounding adhesive mass into firm contact with the bore wall.